Ray Dalio, the head of Bridgewater Associates, is cooling off on his opinion of President Donald Trump.

Dalio, who was hopeful about a Trump presidency and some of his economic policies seems to have struck a less hopeful tone, according to a letter obtained by Bloomberg.

In the letter, Dalio warned that there is a high level of uncertainty in the market and told clients to avoid investing too heavily in a particular asset, according to the Bloomberg report.

"While there is a lot of potential to improve fiscal policies and make beneficial structural reforms (to enhance the business friendly environment, reduce regulatory inefficiencies, etc.), there is also significant risk that his populist policies could hurt the world economy (and worse)," said Dalio in the letter.

It's a quick turnaround for Dalio after the head of the world's largest hedge fund said in a note after the election that Trump's policies could be beneficial to business and the US.

"A pro-business US with its rule of law, political stability, property rights protections, and (soon to be) favorable corporate taxes offers a uniquely attractive environment for those who make money and/or have money," wrote Dalio in December.

Since then, it does appear that some of the trade policies coming from the Trump White House — from a 20% border tax suggestion, strained relations with Mexico's president over NAFTA and a border wall, and attacks on China and Germany over their currencies — seems to have cooled Dalio on Trump.

"Nationalism, protectionism and militarism increase global tensions and the risks of conflict. For these reasons, while we remain open-minded, we are increasingly concerned about the emerging policies of the Trump administration," said the letter from Dalio, according to Bloomberg.